What will cause that you go securely?
R. Yonah: When you guard the entire Torah. However, if you transgress one of its matters, you must fear. This is why it says "Az"! You will be saved from enemies, and from stumbling and falling.
Malbim: Hashgachah will accompany you and guard you from every mishap, in three situations. (a) When you go on the road - then one can be harmed via plunderers, ambushers and murderers. (b) In your house - this includes sleeping, which is more dangerous than while awake, and also while awake, at a time of fear and disaster, guarding is needed. Also the Torah discusses "v'Dibarta Bam b'Shivtecha b'Veisecha uv'Lechtecha va'Derech uv'Shachbecha [uv'Kumecha]" (Devarim 6:7). Here it teaches that you will be guarded at a time of danger, and even when there is little danger. In every case, you will trust in Hashem and not fear, and He will guard you from every mishap - "Ki Mal'achav Yetzaveh Lach
What is the meaning of "Lo Sigof"?
Rashi: Is an expression of stumbling. The same applies to "Pen Tigof ba'Even", "v'Nagefu Ishah Harah" (Shemos 21:22).
